High-density bond pad layout arrangements for semiconductor dies, and connecting to the bond pads

ABSTRACT

Composite bond pad structure and geometry increases bond pad density and reduces lift-off problems. Bond pad density is increased by laying out certain non-square bond pads which are shaped, sized and oriented such that each bond pad closely conforms to the shape of the contact footprint made therewith by a bond wire or lead frame lead and aligns to the approach angle of the conductive line to which it is connected. Alternating, interleaved, complementary wedge-shaped bond pads are discussed. Bond pad liftoff is reduced by providing an upper bond pad, a lower bond pad and an insulating component between the upper and lower bond pads. At least one opening is provided through the insulating component, extending from the bottom bond pad to the upper bond pad. The at least one opening is aligned with a peripheral region of the bottom bond pad and is filled with conductive material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of commonly-owned U.S. patentapplication Ser. No. 08/251,058, filed May 31, 1994, now U.S. Pat. No.5,441,917: which was a divisional of U.S. patent application Ser. No.07/995,644, filed Dec. 18, 1992, now U.S. Pat. No. 5,404,047; which wasa continuation-in-part of U.S. patent application Ser. No. 07/935,449,filed Aug. 25, 1992(now U.S. Pat. No. 5,300,815); which was acontinuation-in-part of U.S. patent application Ser. No. 07/916,328,filed Jul. 17, 1992 (now U.S. Pat. No. 5,340,772) and U.S. patentapplication Ser. No. 07/947,854, filed Sep. 18, 1992 (now U.S. Pat.No.5,248,903).

TECHNICAL FIELD OF THE INVENTION

The invention relates to making connections to integrated circuit (IC)devices (semiconductor dies), particularly to the design, layout,configuration and fabrication of bond pads on the die.

BACKGROUND OF THE INVENTION

Today's semiconductor technology has been advancing in a direction thatrequires ever increasing numbers of interconnections with integratedcircuits. Typically a large number of integrated circuits are formed ona silicon wafer, then are sliced into individual integrated circuit dies(or chips). Each die is then packaged and used.

Electrical connections to the dies are made in one of a few ways. In onetype of package, a die-receiving area (or die receiving cavity) isprovided in the package to receive an integrated circuit die. A numberof conductive lines (traces or leads) whose outer ends are electricallyconnected to pins or leads on the package extend inward towards the diereceiving area, usually in a radial pattern, stopping just short of theperiphery of the die. The die has a number of "bond pads" for thepurpose of making electrical connections with the inner ends of theconductive lines, and is mounted such that the bond pads are exposed.The inner ends of these conductive traces or leads are disposed suchthat they form an array of connection points surrounding the die. Verythin "bond wires" (usually formed of aluminum or gold) are then used toconnect the connections points on a one-for one basis with the bond padson the integrated circuit die. Each bond wire has an "approach angle" tothe die. After mounting, the area or cavity containing the die and thebond wires is usually sealed with a cover or an encapsulant to protectthe die and the bond wires from ambient moisture or physical damage.

In another type of package, exemplified by Tape Automated Bonding (TAB)packaging, a lead frame is provided having a plurality of conductiveleads (sometimes with a tape backing). The lead frame has adie-receiving area, where the semiconductor die is mounted. The leadstypically approach and enter the die-receiving area in a radial pattern,with their inner ends extending within the periphery of the die. The dieis provided with a pattern of "bond pads". The inner ends of the leadsand/or the bond pads are typically provided with solder (or gold) bumps.The die is mounted such that the bond pads align with and makeelectrical contact with the inner ends of the leads. Evidently, in TAB,or other similar technique of connecting dies to leads (or traces), bondwires are not employed.

Often, an integrated circuit die may be used in one of several differentpackages. For example, the same die may be packaged in a plastic orceramic DIP package (dual inline package), a leadless chip carrier(LCC), a plastic leaded chip carrier (PLCC), etc. While these packagesall have a die-receiving area and conductive traces, the arrangement ofconductive traces in the die-receiving area may be slightly differentfrom one package to another. As a result, the approach angle of a bondwire (e.g.) extending to any given bond pad on the die from acorresponding conductive trace may vary somewhat from package topackage.

As mentioned before, "conductive traces" are generally printed traces ona ceramic substrate or on a printed circuit board. "Conductive leads"are usually conductors in a lead-frame, such as in a TAB orplastic-molded package. For the purposes of this specification, the term"conductive lines" will be used hereinafter to refer collectively toconductive leads, conductive traces, and bond wires.

FIG. 1 shows a portion of a typical semiconductor device package 100 ofthe prior art. A die 106 is mounted in a die-receiving area 104. Aroundthe periphery of the die-receiving area 104 is a raised surface 102 witha number of conductive traces 110.

These traces 110 are shown along only one side of the die, forillustrative clarity, but are usually disposed along all (four) sides ofthe die- receiving area 104. A series of square bond pads 108 arearranged along the edges of the die. Again, FIG. 1 shows bond pads alongonly one edge of the die for illustrative clarity, but bond pads areusually provided along all of the edges of the die, on the "top"(circuit element containing) surface of the die just within the edges ofthe die. Bond wires, e.g., 112a, 112b, 112c, 112d and 112e, connectrespective conductive traces 110 (e.g., 110a, 110b, 110c, 110d and 110e)to respective bond pads 108 on a one-to-one basis. The conductive tracesapproach the die 106 in a generally radial pattern (fanned-out, orfanned-in pattern), such that the "approach angles" of conductive tracesand bond wires closest to an end of die edge 118 (e.g., 110d, 112d,110e, and 112e) are the furthest off-perpendicular, while the approachangles of conductive traces and bond wires nearest the center (midpoint)of the die edge 118 (e.g. 110a and 112a) are substantially perpendicularto the edge 118, with the off-perpendicular component of approach anglesgenerally increasing with the offset from the midpoint of the die edge.A centrally located conductive trace 110a and bond wire 108a approachthe die such that their approach angle (as shown by dashed line 114) issubstantially perpendicular to the edge 118 of die 106. Anotherconductive trace 110b and bond wire 112b, located three traces (and bondwires) away from the centrally located conductive trace 110a (and bondwire 112a), approaches the die 106 at an off-perpendicular angle φ₃. Yetanother conductive trace 110c and bond wire 112c, located nine traces(and bond wires) away from the centrally located conductive trace110a(and bond wire 112a), approach the die at an off-perpendicular angleφ₉ (greater than φ₃.

FIG. 2 shows a more detailed view of the die 106. A typical bond wire112 is shown attached to a typical square bond pad 108. An inter-padspacing of "d" is shown, between bond pads. The bond wire 112 enters thepad area at an approach angle Θ. The contact area ("footprint") 220formed by the bond wire 112 with the bond pad 108 is generallyelliptical. This is typical of contact footprints between bond wires andbond pads which usually have an elongated shape, with the "elongateddimension" (or "major axis" of the shape, defined hereinbelow)substantially aligned with the approach angle (φ).

Typically, prior art bond pads are square, as shown in FIGS. 1 and 2,and are capable of receiving bond wires over a wide range of approachangles, since a bond pad is typically much larger (e.g., in overallarea) than the contact footprint formed by the bond wire (or, forexample, by an analogous conductive lead in a TAB package).

As stated hereinabove, there is a great deal of pressure in modernintegrated circuit technology to provide greater numbers ofinterconnections (I/O) to integrated circuit dies. This, of course,requires a commensurate increase in the number of bond pads disposedabout the periphery of the die. As mentioned hereinabove, there istypically a required minimum inter-pad spacing "d" between adjacent padsto minimize the possibility of shorting or coupling between adjacentbond pads or bond wires (or conductive leads). And, it virtually goeswithout saying, that the size of bond pads cannot readily be reduced.However, there is a finite, limited amount of space (linear area) alongthe edges of an integrated circuit die for accommodating bond pads. Thisevidently limits the number of bond pads that can be arranged along theedges of the die. One approach to increasing the number of bond pads,and hence the number of connections that can be made to the die, is toprovide multiple (e.g., two) rows of bond pads along the edges of thedie, but this approach would require bond wires to cross over oneanother, creating a serious risk of a short circuit, even if the rows ofbond pads were staggered. (Such a multiple row approach is somewhatinapposite for TAB.) This problem is especially poignant in cases wherethere is a wide range of approach angles to bond pads possible fordifferent packages.

The present invention is also concerned with the formation (structure)of the bond pad itself, irrespective of the approach angle or I/O count(number of bond pads that fit along the edge of a die) situationsdiscussed above.

Integrated circuit devices comprise a semiconductor die having a varietyof diffusions and overlying layers forming circuit elements, gates andthe like. Generally, the penultimate layers fabricated on the die areconductive metal layers ("M") having patterns of conductive lines.(These conductive lines are internal to the die, and should not beconfused with the leads and traces discussed hereinabove, which areexternal to the die.) Two or more metal layers ("M1", "M2", etc.) areseparated by a dielectric layer of inter-layer dielectric (ILD). Forpurposes of this discussion, it is assumed that there are two conductivelayers, a layer designated "M1", and a layer designated "M2". An ILDlayer overlies the M1 layer, and the M2 layer overlies the ILD.Typically, a topmost passivation layer is applied over the M2 layer.Openings through this passivation layer expose areas of the M2 layer.These exposed areas are termed "bond sites". The "bond pad", per se, isthe bond site, and the underlying M2/ILD/M1 structure. Connections tothe die, hence to the circuitry contained on the die, are effected withthese exposed areas (i.e., bond pads). For example, bond wires may bebonded directly to the bond sites (pads), or solder or gold bumps may beformed on the bond sites for tape-automated bonding to the die, or goldballs may be formed on the exposed areas for flip-chipping the die to asubstrate. This is all well known.

As mentioned above, the bond pad is ultimately bonded to, whether with abond wire or the like (e.g., solder or gold bumps). These variousprocesses typically impart mechanical and or thermal energy directlyonto the bond pad, especially in the contact area. It has been observedthat these bonding processes can cause the bond pad to delaminate (lift)from the underlying surfaces of multiple metal layers and oxide. Thisbond pad lift problem can happen in all different kinds of bondingtechnology, such as aluminum wire bond, gold ball bonding, gold bumpbonding, and 5 others. This bond pad lift problem can become exacerbatedwhen there is layer of barrier metal, such as titanium (Ti), titaniumnitride (TIN), Titanium-Tungsten (TiW), and the like, under the bondpads. Bond pad lift is very undesirable, and can result in potentialproblems in both assembly (packaging) yield and device reliability.

In the past, efforts to alleviate bond pad lift have been directed to:(1) adjusting bonding process parameters to minimize the thermal and/ormechanical shock to the bond pad; and (2) optimizing the barrier metallayer materials and deposition technology. These efforts have met withonly partial success, and impose undesirable constraints (i.e., a narrowwindow of process parameters) on the bonding process.

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to provide atechnique for increasing the number of bond pads on an integratedcircuit (semiconductor) die, especially on a semiconductor die having agiven periphery.

It is another object of the present invention to provide bond pads whichcan accommodate a wide range of approach angles.

It is a further object of the present invention to provide a techniquefor increasing the number of bond pads on an integrated circuit diewhich can be accomplished in a single row of bond pads.

It is a further object of the present invention to provide an improvedbond pad structure for semiconductor devices.

It is a further object of the present invention to reduce bond pad lift,without narrowing the window of bonding process parameters.

According to the invention, elongated or "certain non-square" compositebond pads, described hereinbelow, which conform closer to a contactfootprint shape than do prior-art bond pads, permit closercenter-to-center spacing of bond pads that do prior-art square bondpads, while maintaining comparable inter-pad spacing.

In one embodiment of the invention elongated bond pad shapes are definedwhich conform roughly to the shape of a contact footprint. Bond padshaving this shape are then disposed along a side of an integratedcircuit die and oriented such that they substantially align with theconductive lines to which they will be connected.

In another embodiment of the invention, the side of the die is astraight edge, and the bond pads are arranged to align with a radial or"fanned" pattern of conductive lines.

In another embodiment, the semiconductor die is further adapted to bemounted in a die receiving area of a substrate, such as a ceramicpackage, a printed circuit board, or a TAB package, and the bond padsare shaped and aligned to the approach angle and contact footprint ofthe conductive lines to be connected thereto.

In various embodiments, the conductive lines may be bond wires,conductive traces, or conductive leads.

In another embodiment, the bond pad shapes are defined by defining acontact footprint shape, choosing an elongated shape and sizing it suchthat it encloses the contact footprint shape. Another embodimentelaborates on this technique by providing a safety zone around thecontact footprint shape to allow for errors in placement, approachangle, or variations in contact footprint shape. The elongated shape isthen sized to enclose the safety zone.

Other embodiments provide for specific elongated shapes, includingelongated rectangular shapes, parallelogram shapes, trapezoidal shapes,tapered shapes, and non-polygonal curved shapes (for example,elliptical, cardioid, trochoid, or "egg-shaped" curves).

In another embodiment of the invention, "certain non-square" bond padshapes are defined by defining a pivot point in a contact footprint,defining a "swept contact area" by rotating (sweeping) the contactfootprint through a range of angles, then shaping and sizing a polygonalor curved shape to closely conform to and enclose the swept contactarea. Another embodiment adds to this technique by adding a safety zonearound the swept contact area and additionally requiring that the bondpad further enclose the safety zone. Still another embodiment defines an"anchor point" within the bond pad shape according to the location ofthe pivot point in the swept contact area around which the bond padshape was defined.

Often, "certain non-square" shapes will have a sort of "wedge" shape tothem, particularly if the pivot point is defined off-center of theelongated contact footprint. It is also possible to move the pivot pointto the other end of the contact footprint to generate complementaryshapes. The possibility of complementary shapes suggests the possibilityof arranging such shapes in an alternating interleaved linear array,providing the benefits of both higher bond pad density and a wide rangeof approach angles.

Other embodiments of the invention deal with arranging alternatinginterleaved arrays of bond pads along one or more edges of asemiconductor die.

Another embodiment of the invention provides for connecting bond wiresto alternating interleaved arrays of bond pads by allowing foralternating locations of anchor points on bond pads and different pivotpoints (mounting reference points relative to the ends) on bond wiresdepending upon the bond pads to which they will be connected.

The observation can be made that the actual bond pad space used by abond wire is the area covered by the contact footprint made by the bondwire with the bond pad. Allowing a safety zone outside of this space forvariations in contact footprint from bond pad to bond pad, and forslight error in placement and approach angle, it can be seen that theminimum required area of a bond pad is only slightly larger than thecontact footprint. Since the contact footprint is usually an elongatedshape substantially aligned with the approach angle of the bond wire, asimilarly shaped and oriented bond pad (elongated bond pad) may be used.This sort of bond pad requires significantly less space along an edge ofa die than the bond pads of the prior art, and complementary angledshapes may be nested to take up even less space.

Further according to the invention, a composite bond pad includes anupper bond pad, a lower bond pad and an insulating component between theupper and lower bond pads. At least one opening is provided through theinsulating component, extending from the bottom bond pad to the upperbond pad. This at least one opening is aligned with a peripheral regionof the bottom bond pad. Conductive material fills the at least oneopening, and electrically connects the top and bottom bond pads.

In one embodiment of the invention, the at least one opening is aplurality of vias. Each via may measure approximately one micron incross-section. The vias may extend in at least one "string" (row) aroundthe peripheral region of the lower bond pad. If there are two or morestrings of vias, the vias of one string are preferably offset from thevias of another adjacent string.

In another embodiment of the invention, the at least one opening is aring-like opening extending around the peripheral region.

In yet another embodiment of the invention, the at least one opening isone or more elongated slit-like openings. In the case of two of theseelongated slit-like openings, they may be disposed across from oneanother vis-a-vis the area defined by the lower bond pad.

Other objects, features and advantages of the invention will becomeapparent in light of the following description thereof.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a plan view of a typical prior art bond pad arrangement andbond wire connections thereto.

FIG. 2 is a plan view of a typical attachment of a bond wire to a bondpad according to the prior art.

FIGS. 3a-3c are plan views of various approaches to increasing bond paddensity, according to the present invention.

FIG. 4 is a plan view of an integrated circuit die employing the presentinventive technique.

FIG. 5 is a view of a section of an integrated circuit die showing theorientation of a tapered bond pad, according to the present invention.

FIGS. 6a-6d are plan views of bond pads showing the relationship betweenthe contact pattern made by a bond wire with a bond pad, the approachangle, "anchor points" and bond pad shape, according to the presentinvention.

FIGS. 7a-7b are plan views of bond pads, showing an application of analternating interleaved arrangement of complementary polygonal bond padshapes, according to the present invention.

FIGS. 7c and 7d are plan views of bond pads employing a technique forminimizing the risk of shorting and coupling between bond wires andadjacent bond pads, according to the present invention.

FIG. 7e is a plan view of non-polygonal curved bond pads showing the useof complementary curved shapes for an alternating interleavedarrangement of bond pads, according to the present invention.

FIG. 8a is a cross-sectional view of a prior art bond pad.

FIG. 8b is a plan view of the bond pad of FIG. 8a.

FIG. 9a is a cross-sectional view of an embodiment of a bond padaccording to the present invention.

FIG. 9b is a top plan view of the bond pad of FIG. 9a.

FIG. 10a is a top diagrammatic view of another embodiment of a bond pad,according to the present invention.

FIG. 10b is a top diagrammatic view of yet another embodiment of a bondpad, according to the present invention.

FIG. 10c is a top diagrammatic view of yet another embodiment of a bondpad, according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Bond Pad Shape

In general, the present invention makes use of elongated bond pads whichgenerally conform to the shape of the elongated contact footprints madeby bond wires (or by conductive leads) attached to the bond pads, takinginto account slight errors in placement, variations in contactfootprint, and variations in approach angle which may occur during thebonding process.

FIGS. 3a -3c show various possible bond pad shapes and arrangementsaccording to the present invention. For all of these FIGS. 3a-3c, auniform approach angle is assumed. (In other words, all of the bondwires approach bond pads at the same angle with respect to the edge ofthe die.)

FIG. 3a shows a series of elongated parallelogram-shaped bond pads 306arranged on a die 106 such that a minimum distance "d" is maintainedbetween adjacent bond pads. These bond pads are each designed toaccommodate a bond wire, such as bond wire 304, having an approach angleΘ. The geometric shape of the bond pad 306 is determined by providingsufficient area to accommodate not only a contact footprint 304a, butalso a "safety zone" area 304b around the contact footprint 304a, thenfitting a parallelogram to (around) the resulting area requirement. Thesafety zone 304b allows for some (predetermined) error in placement ofthe bond wire (or more generally, the conductive line), allows for someerror in the approach angle, and allows for some variation in the shapeor size of the contact footprint. The slanted sides 306a of the bondpads 306 are substantially aligned with the approach angle Θ of the bondwire 304 and take up significantly less space than do the square bondpads 108 of the prior art. (The bond pads 108 of the prior art are shownin dashed lines for size comparison.) Square bond pads 306 have the sameheight "h" as do the parallelogram shaped bond pads 306, but have awidth equal to their height. The same spacing "d" is maintained betweenadjacent square bond pads and adjacent parallelogram shaped bond pads,as shown in the Figure.

In this example, four parallelogram shaped bond pads 306 require justabout the same peripheral area of the die as do three comparable squarebond pads 108, thus providing approximately a 33% increase in bond paddensity (count) over square bond pads, hence allowing for a greaternumber of electrical (I/O) interconnections to the die.

The parallelogram shaped bond pads 306 in FIG. 3a have four straightedges. It is often desirable, for simplicity of layout, to have one ofthe bond pad edges parallel to the edge 118 of the integrated circuitdie, and to have an opposing edge parallel thereto. In this manner, theouter (i.e., towards the die edge) edges of the bond pads can beestablished to lie along a line parallel to the corresponding edge ofthe die, and the opposite, inner edges of the bond pads lie will alsolie along a line parallel to the corresponding edge of the die. Whenapproach angles are not perpendicular to the edge of the die, and theelongated bond pad is oriented along the direction of the approachangle, this can result in a bond pad shape, orientation and layout suchas that of the parallelogram shape shown in FIG. 3a.

FIG. 3b shows an alternate embodiment of bond pads 306' accommodatingbond wires 304, according to the present invention. In this case, asomewhat diamond shaped bond pad is used, similar to the parallelogramshaped bond pads of FIG. 3a. However, portions (namely corners) of thepads 306' lying outside of the safety zone are "trimmed" to provide theshape shown. As in FIG. 3a, a minimum space "d" is maintained betweenadjacent bond pads. Each bond pad has a long dimension "1" and a shortdimension "w". The bond pad is oriented such that the short dimension ismaintained generally perpendicular to the approach angle Θ of the bondwires 304, also indicated by line 310. In this example, the approachangle and the long dimension of the bond pad are aligned, since the longand short dimensions of the bond pad are perpendicular to one another.However, this is not necessarily the case with all elongated shapes.Parallelograms, for example have long and short dimensions which are notnecessarily perpendicular to one another. Preferably, as illustratedherein, the short dimension of the bond pad is maintained perpendicularto the approach angle, which works for many elongated bond pad shapes.

FIGS. 3a and 3b are illustrative of some polygonal bond padconfigurations, according to the present invention. Further polygonalconfigurations are set forth hereinbelow.

FIG. 3c illustrates non-polygonal bond pads, according to the presentinvention. In this case elliptical bond pads 306" are used. The majoraxis 310 of the ellipse shape is aligned with the approach angle Θ ofthe bond wire. The same spacing (d) between bond pads is maintained asin FIGS. 3a and 3b. The bond pad may be any suitable curved shape whichcan be circumscribed about the established safety zone (see, forexample, 304b with respect to FIG. 3a) surrounding an elongated contactfootprint, including a shape that is substantially similar to the shapeof the safety zone.

The assumption is made herein that the contact footprint made by a bondwire with a bond pad is aligned with the approach angle. It is possiblethat for some bond wire attachment schemes the contact footprint may beslightly differently oriented. For those schemes, the different(non-uniform) contact footprint orientation must be taken into account.However, as long as a contact footprint has an elongated shape, theprinciple of shaping bond pads to accommodate the contact footprint maybe applied to provide increase bond pad density on dies.

FIGS. 3a-3c have shown various bond pad shapes oriented to accept bondwires arriving at a constant approach angle. However, in reality, bondwires-approach from a number of different angles, as is illustrated inFIG. 1.

FIG. 4 shows a typical die 402 employing the technique of the presentinvention as applied to a radial pattern of conductive lines (or bondwires) 406a . . . n. Each conductive line 406a . . . n may have its ownunique approach angle αa . . . n. Each bond pad 404a . . . n is alignedto the approach angle of the corresponding conductive line 406a . . . n(or to the angle of the contact footprint made therewith, if theorientation of the contact footprint differs from the approach angle ofthe conductive line). As shown, conductive lines 406 approach (fan-intowards) the die 402 in a generally radial pattern.

In order for bond pads to align with a radial pattern of conductivelines while maximizing the number of bond pads which will fit on a die,it is advantageous to use an elongated tapered pad shape. The bond pads404a . . . n shown in FIG. 4 taper slightly towards the center of thedie 402, as illustrated in greater detail in FIG. 5.

FIG. 5 shows a tapered bond pad 502 having tapered sides 502a and 502bon a die 501. The bond pad 502 is oriented such that it aligns with anapproach angle Θ_(APPROACH) measured between major axis 504 of bond pad502 and an edge 501a of die 501. Axis 504 indicates the line along whicha bond wire or other conductive line will approach the bond pad 502. Iflines are extended from tapered sides 502a and 502b, they willeventually meet at a point 506, defining a taper angle Θ_(t). Ideally,the axis 504 should bisect this angle, as shown, indicating the idealangle of approach to tapered bond pad 502. Accordingly, tapered bond pad502 would be oriented on the die 501 such that its axis 504 aligns withthe anticipated approach angle. If a small range of approach angles isanticipated (as indicated by dashed lines 504a and 504b), and assumingthat the bond pad 502 has been sized to accommodate a range of approachangles, then the axis 504 should bisect that range, as shown.

The discussion above with respect to FIGS. 4 and 5 assumes that themajor axis of a contact footprint (the line perpendicular to its minimumoverall dimension) is in perfect alignment with the approach angle ofthe conductive line with which it is made. For some methods ofattachment, however, there may be an offset between the approach angleof the conductive line and the major axis of the contact footprint. Inthese cases, the same technique described hereinabove may be used byproviding a compensation for this offset in the orientation of the bondpads. That is, use the major axis of the anticipated contact footprintas the approach angle.

All of the bond pads discussed hereinabove with respect to the presentinvention have, by definition, an "elongated" shape. This is becausethey have an overall width in a direction generally perpendicular to anexpected approach angle which is significantly less than their overalllength along the approach angle. That is, they are long along theanticipated approach path of a bond wire, and narrow across that sameapproach path. This permits more of these shapes to be arranged alongthe edge of an integrated circuit die than could be arranged usingprior-art square bond pads (compare, e.g., FIGS. 1 and 2).

The discussion hereinabove with respect to FIGS. 1-5 indicates thatindividual conductive lines (including bond wires) may approach from arange of angles, but the designs of individual bond pads have been for afairly precise approach angle, allowing only for small errors inplacement or approach angle.

FIGS. 6a-6d illustrate the design of bond pads, according to the presentinvention, where a wider range of approach angles may be encountered atany individual bond pad.

FIG. 6a shows a simple rectangular bond pad 606 designed to accommodatean elliptical contact footprint 602 having a major axis 608 and a minoraxis 610. A safety zone 604 is allocated around contact footprint 602,and then rectangular bond pad 606 is sized to fit exactly around thesafety zone 604. One of the two short edges of the bond pad is orientedtowards the edge of the die.

For size comparison, a square bond pad 606a of the prior art is shownoverlaid in dashed lines. This is a particularly good comparison,because the square bond pad 606a represents a minimum-size square bondpad. Evidently, the rectangular bond pad permits a greater number ofbond pads to be placed along an edge of a die than does the prior-artsquare bond pad.

FIG. 6b shows a rectangular bond pad 606' designed to accommodate a widerange of approach angles. Contact footprint 602 (made by an electricalconnection to a bond pad by a conductive line) is shown in its nominalposition. Contact footprints 602x and 602y represent the orientation ofcontact footprint 602 if rotated about a point 612 through angles ofΘ_(x) and Θ_(y), respectively. The pattern formed by "sweeping" thecontact footprint 602 through its possible range of approach anglesdefines the shape and size of a swept contact area 603 which must beallocated on the bond pad for attachment of the conductive line. Asafety zone 604' is allocated around the allocated swept contact area toallow for slight errors in placement and variation in contact footprint.Finally, a rectangular bond pad shape 606' is determined bycircumscribing a rectangle around safety zone 604'. The major axes 608,608x, and 608y of contact footprints 602, 602x, and 602y, respectively,illustrate the range of approach angles for which pad 606' is designed.

A similar approach may be applied to bond pads of other shapes,according to the present invention--for example, tapered pads,parallelogram shapes, curved shapes, etc., resulting in bond pad shapesthat will' be referred to hereinafter as "certain non-square" shapes.

In the extreme, where the range of approach angles for a given bond padis very wide (e.g., +/-45 degrees and greater), the shape of therectangular (or other shape) bond pads 606' formed as described withrespect to FIG. 6b, widens and may become arbitrarily similar to theshape of prior-art square bond pads (e.g., 606a, FIG. 6a), providing nobenefit thereover. Evidently, then, there is still a need for atechnique which provides both higher bond pad density and accommodationof a very wide range of approach angles)

FIGS. 6c and 6d show different bond pad shapes which are derived fromchanging the pivot point used to determine the swept contact area.

In FIG. 6c, the contact pivot point 612' is moved upward in contactfootprint 602 relative to its location 612 in FIG. 6b yielding adifferently shaped swept contact area outline 603'. Contact footprints602x' and 602y' represent the position of contact footprint 602 whenrotated about pivot point 612' through angles of Θ_(x), and Θ_(y),repectively, as measured from the major axis 608 of contact footprint602 to the major axes 608x' and 608y' of rotated contact footprints602x' and 602y', respectively. Allowing for a safe zone (not shown)around swept contact area 603', a convenient polygonal shape is chosenfor bond pad 614. This trapezoidal shape matches well with the shape ofthe swept contact area outline 603' and does not leave a great deal ofunallocated space. Alternatively, the triangle shape indicated by addingthe area 614a to the trapezoidal bond pad 614 could be used. However,the additional area would be of no benefit for the immediate purposes ofthe present invention.

In FIG. 6d, the contact pivot point 612" is moved downward in contactfootprint 602 relative to its location 612 in FIG. 6b yielding a yetanother differently shaped swept contact area outline 603", which isessentially a vertical mirror image of swept contact area outline 603'with respect to FIG. 6c. Contact footprints 602x' and 602y' representthe position of contact footprint 602 when rotated about pivot point612" through angles of Θ_(x), and Θ_(y), respectively, as measured fromthe major axis 608 of contact footprint 602 to the major axes 608x" and608y' of rotated contact footprints 602x" and 602y", respectively.Allowing for a safe zone (not shown) around swept contact area 603", apolygonal shape similar to that of bond pad 614 is chosen for bond pad616. Again, this trapezoidal shape matches well with the shape of theswept contact area outline 603" and does not leave a great deal ofunallocated space.

The following definitions may be used herein:

Conductive line: A bond wire, conductive trace, or conductive lead usedfor direct connection to a bond pad on an integrated circuit die.

Bond pad: An electrical connection point located along an edge of anintegrated circuit die.

Contact footprint: The shape of the contact area made between aconductive line and a bond pad.

Elongated contact footprint: An asymmetrical contact footprint which hasa length which is greater than its width. Elongated contact footprintshave a major axis aligned such that their dimension perpendicular to theaxis is as small as possible.

Contact pivot point: A point of reference on a contact footprint aboutwhich it is rotated to generate a swept contact area.

Anchor point: A point of reference on a bond pad for connecting toconductive lines.

Expected contact footprint: The contact footprint expected to be formedwhen a conductive line is connected to a bond pad.

Certain non-square bond pad: A bond pad that is not square, and thatsubstantially-conforms to a shape that encloses an area defined by therotation of an elongated contact footprint through a limited range ofangles about a "contact pivot point".

Bond pad axis: Defined by the axis of the elongated contact footprintused to define a "certain non-square" bond pad when at the middle of itsrange of rotation about the contact pivot point.

Approach angle: The angle a conductive line connected to a bond padmakes with the edge of the integrated circuit die along which the bondpad is located. "Expected approach angle" refers to the approach anglefor which a bond pad is designed. In the event that the major axis of acontact footprint is not aligned with the approach angle of a conductiveline, then the angle of the major axis of the contact footprint is takenas the approach angle.

Major Axis of a bond pad: The line centered in the expected range ofapproach angles. This line runs through the anchor point on "certainnon-square" bond pads.

Elongated bond pad: A bond pad for which the length along its major axisis greater than its maximum width perpendicular to its major axis by aratio of at least, for example, 20%, 30%, 50%, 70%, or 100%.

Examples of "certain non-square" bond pad shapes are: "elongated"rectangles (i.e, rectangles having an aspect ratio of greater than1.2:1), triangles, trapezoids (truncated triangles), parallelograms,ellipses, or any other suitable polygonal or curved shapes.

According to a feature of the invention, every "certain non-square" bondpad has an associated anchor point, expected contact footprint, andcontact pivot point. For any approach angle a conductive line will bemounted such that the contact pivot point of the expected contactfootprint aligns with the anchor point of the bond pad.

Generally, when the contact pivot point is placed away from the centerof the contact footprint, the result will be a "certain non-square" bondpad shape which is wide on one end and narrow on another end. As shownin FIGS. 6c and 6d, it is possible to come up with complementary bondpad shapes (e.g., 614 and 616). It would appear that bond pad shapes 614and 616, which are complementary to one another, might be useful ifarranged in an alternating interleaved pattern. This arrangement isshown in FIGS. 7a and 7b.

In FIG. 7a, bond pads 702a, 702b, 702c, and 702d are arranged in analternating interleaved array, as shown, where bond pads 702a and 702c(similar to 614 with respect to FIG. 6c) have similar shapescomplementary to the shapes of bond pads 702b and 702d (similar to 616with respect to FIG. 6d). Bond pads 702a, 702b, 702c, and 702d haveanchor points located at 703a, 703b, 703c, and 703d, respectively,reflective of the manner in which each shape was derived (refer to FIGS.6c, 6d). In order to illustrate the method of connection of bond wiresto these bond pads, bond wires 704a, 704b, 704c, and 704d, are shownapproaching bond pads 702a, 702b, 702c, and 702d, respectively, atapproach angles near one extreme of the anticipated range of approachangles used to design the bond pads. The connection of bond wires 704a,704b, 704c, and 704d to bond pads 702a, 702b, 702c, and 702d, formscontact footprints 706a, 706b, 706c, and 706d, respectively therewith.The bond wires are mounted such that the contact pivot point of contactfootprint 706a aligns with the anchor point 703a of bond pad 702a, thecontact pivot point of contact footprint 706b aligns with the anchorpoint 703b of bond pad 702b, the contact pivot point of contactfootprint 706c aligns with the anchor point 703c of bond pad 702c, andthe contact pivot point of contact footprint 706d aligns with the anchorpoint 703d of bond pad 702d.

FIG. 7b shows the same bond pads 702a, 702b, 702c, and 702d, and thesame bond wires, 704a, 704b, 704c, and 704d, but this time the bondwires have a different approach angle, near the opposite end of theexpected range of approach angles from that used in FIG. 7a. Coming fromthis approach angle, bond wires 704a, 704b, 704c, and 704d, make contactfootprints 706a', 706b', 706c' and 706d' respectively. The contactfootprints 706a, 706b, 706c, and 706d are superimposed and shown asdotted lines for comparison.

The bond pad arrangements of FIGS. 7a and 7b may encounter problems withshorting or coupling with adjacent bond pads if the bond wires do notarch significantly over the surface of the integrated circuit die beforeattaching to the bond pads. Note for example the location 720a withrespect to FIG. 7a where bond wire 704b closely approaches a corner ofbond pad 702a. Also note with respect to FIG. 7b the location 720b wherebond wire 702bclosely approaches a corner of bond pad 702c.

One approach to solving this problem is to increase the spacing betweenall bond pads, but this approach would significant reduce the effectivebond pad density, eliminating much of the benefit of the presentinvention.

A more attractive approach to solving this problem is shown in FIG. 7c,whereby corners 712 of bond pads 712a and 712c are eliminated, yieldingmodified bond pads 702a' and 702c'. With the elimination of thesecorners, the potential interference between bond wires and neighboringbond pads is eliminated. Note that modification of bond pads 702b and702d is not necessary, since the corresponding corners of these bondpads, which are oriented away from the approach path of the bond wires,do not pose a risk of shorting. However, for uniformity (implyingsimplicity of layout) and to minimize coupling between adjacent bondpads, it may be desirable to modify bond pads 702b and 702d as well.

FIG. 7d shows this situation, where all bond pads have the modifiedshape, including modified bond pads 702b' and 702d'.

An alternative approach is shown in FIG. 7e, where non-polygonal curvedshapes closely following the shape of the swept contact area (see FIGS.6c and 6d) are used for bond pads 702a", 702b", 702c" and 702d". Thesebond pads have many of the same benefits discussed hereinabove, e.g.,improvement of bond pad density, minimal risk of shorting or couplingbetween bond wires and adjacent bond pads, minimal coupling between bondpads, etc.

This approach of using interleaved bond pads requires that the methodused to mount bond wires to such pads must take into account the varying(alternating) locations of anchor points relative the edge thesemiconductor die and pivot points relative to the contact footprintsthat will be made with the bond wires. This requires that thewire-connecting method must use different points of reference on thebond pads and bond wires, depending upon which type of bond pad is to beconnected to.

The concept of using interleaved bond pads, while shown with bond wires,is equally applicable to the other types of conductive lines discussedhereinabove, such direct attachment of bond pads to conductive leads ortraces (e.g., leadframe attachment as in TAB packages).

With "certain non-square" contact shapes and alternating interleavedlinear arrays of bond pads, as with elongated bond pads, the discussionhereinabove generally assumes that the major axis of a contact footprintis in perfect alignment with the approach angle. In cases where there isan offset angle between the major axis of the contact footprint and theapproach angle, the same technique described hereinabove may be used byproviding a compensation for this offset in the orientation of the bondpads, without loss of generality. That is, use the major axis of theanticipated contact footprint as the approach angle.

Other aspects of the present invention discussed hereinabove, such asradial patterns of bond pad orientation, tapered bond pad shapes, etc.,may be used either alone or in combination with one another.

Using the techniques of the present invention, it is possible to createintegrated circuits having significantly larger numbers of bond pads,which allow for a greater number of I/O connections and interfacesignals than would be possible using prior art bond pad design for agiven die size. For example, for a given die size of the prior artaccommodating some limited number of bond pads (at a given pad-to-padspacing), the geometric configurations of the present invention willallow a substantial (on the order of 33%; or greater) increase in thenumber of bond pads that can be accommodated (on the same size die). Inother words, whereas only four hundred bond pads could have beenaccommodated in the prior art, by using this invention I/O counts(number of bond pads) in excess of five hundred can readily be achieved.It is within the scope of this invention that semiconductor dies havingin excess of "n" bond pads may be fabricated, where "n" is≧500, 550,600, 650, 700, 750, 800, 850, 900, 950 or 1000.

Bond Pad Construction

FIGS. 8a and 8b illustrate the structure (construction) of a prior art"composite bond pad" 800. Typically, a plurality of such bond pads wouldbe disposed on a die. A partially-fabricated semiconductor die 802,having various diffusions and depositions (not shown), has a top surface803. A layer 804 of insulating material (e.g., silicon dioxide) isformed on the surface 803. A patterned layer 806 of "barrier metal" isapplied over the oxide 804. A patterned conductive layer 808 of "first"metal ("M1") is applied over the barrier metal 806, and is connected(not shown) to circuit elements (not shown) contained on the die. Alayer 810 of inter-layer dielectric ("ILD"; e.g., silicon dioxide) isapplied over the first metal layer 808, and is provided with an opening812 extending through the layer 810 to the top surface (as viewed in theFigure) of the underlying M1 layer. A patterned conductive layer 814 of"second" metal ("M2") is applied over the ILD 810, and a portion 816 ofthis layer 814 forms a conductive "plug" filling the opening 812. Atopmost "passivation" layer 818 (e.g., Borophosphosilicate Glass, orBPSG) is applied over the M2 and ILD layers, and is provided with anopening 820 extending through the passivation layer 818 to the topsurface (as viewed in the Figure) of the underlying M2 layer. Thisleaves an area 820 of the top surface of the M2 layer exposed. The area820 is termed the "contact area" ("bond site"). It is in this contactarea that external connections to the die will be made, by any suitablemeans such as bond wires. Alternatively, gold bumps (not shown) or goldballs (not shown) can be formed atop the area 820, for tape-automated(TAB) bonding or flip-chip bonding to the die.

In aggregate, the elements 814, 816 and 808 comprise the "composite bondpad" 800, which is comparable to the bond pad 108 shown in top view inFIGS. 1 and 2. For purposes of this discussion, the portion of the metallayer 814 above dashed line 815 is termed "upper bond pad", and theportion of the lower metal layer 808 underlying the upper bond pad istermed "lower bond pad". The use of a barrier metal layer (806)underneath the bond pad (i.e., underneath the M1 layer) is optional, andoffers certain protection against diffusion into the M1 layer of"fugitive" species (contaminants, vis-a-vis the M1 layer) fromunderlying layers in the die.

As best viewed in FIG. 8b, the (composite) bond pad 800 is generallysquare (it is shown in the Figure as a slightly elongated rectangle),and has dimensions on the order of 100×100 μm (microns). Further, theupper bond pad may be larger than the "plug" 814. For example, if theupper bond pad measures 100 μm across, the plug may measure only 80-90μm across. As is evident, only the outer peripheral region (for examplethe outermost 10% of the upper bond pad) of the upper bond pad rests onthe ILD 810.

In practice, the lower bond pad element 808 may be a defined portion(shown as a slightly elongated rectangle) of a conductive line of the M1layer.

In practice, a plurality of bond pads (800) are disposed on the topsurface of the die, for making a plurality of input/output (I/O)connections to the die.

As mentioned above, ultimately the contact area 820 (i.e., the bond pad)is bonded to, whether with a bond wire, or by the mechanism of goldbumps/balls. These various processes typically impart mechanical and orthermal energy directly onto the bond pad, especially in the contactarea. It has been observed that these bonding processes can cause thebond pad to delaminate (lift) from the underlying surfaces of multiplemetal layers (e.g., 806) and oxide (e.g., 804). This bond pad liftproblem can happen in all different kinds of bonding technology, such asaluminum wire bond, gold ball bonding, gold bump bonding, and others.This bond pad lift problem can become exacerbated when using anunderlying layer of barrier metal (806), such as titanium (Ti), titaniumnitride (TIN), Titanium-Tungsten (TiW), and the like, under the bondpads. Bond pad lift is very undesirable, and can result in potentialproblems in both assembly (packaging) yield and device reliability.

FIGS. 8a and 8b show a prior art bond pad structure, and have beendiscussed in detail hereinabove. Particularly, the problem of bond padlift, using a large plug (816) between M2 (814) and M1(808), wasdiscussed.

According to the present invention, a connection between M2 and M1 ismade only around a small peripheral portion (band) of the bond pad.

FIGS. 9a and 9b illustrate the structure of the composite bond pad 900of the present invention, which may be any of the novel shapes discussedabove, such as with respect to FIGS. 3a-3c, 4, 5, 6a-6d or 7a-7e. Thetrapezoidal bond pad shape of FIG. 6c is employed for exemplary purposesin the plan views of FIGS. 9b, 10a-10c.

A partially-fabricated semiconductor die 902, having various diffusionsand depositions (not shown), has a top surface 903. A layer 904 ofinsulating material (e.g., silicon dioxide) is formed on the surface903. A patterned layer 906 of "barrier metal" is applied over the oxidelayer 904. A patterned conductive layer 908 of "first" metal ("M1") isapplied over the barrier metal 906, and is connected (not shown) tocircuit elements (not shown) contained on the die. A defined area ofthis M1 layer (best viewed in FIG. 9B) forms the lower bond pad element.A layer 910 of inter-layer dielectric ("ILD"; e.g., silicon dioxide) isapplied over the first metal layer 908, and is provided with a pluralityof small openings (vias) 912 extending through the layer 910 to aperipheral region of the lower bond pad 908. A patterned conductivelayer 914 of "second" metal ("M2") is applied over the ILD 910, and aportion 916 of this layer 914 fills the openings 912. Alternatively, theopenings 912 can be filled by selective deposition of a metal such astungsten. The portion of the layer 914 overlying the ILD 910 is theupper bond pad element. A topmost "passivation" layer 918 (e.g.,Borophosphosilicate Glass, or BPSG) is applied over the M2 and ILDlayers, and is provided with an opening 920 extending through thepassivation layer 918 to the top surface (as viewed in the Figure) ofthe underlying M2 layer. This leaves an area 920 of the top surface ofthe M2 layer exposed. The area 920 is termed the "contact area". As inthe prior art, it is in this contact area (920) that externalconnections to the die will be made, by any suitable means such as bondwires. Alternatively, gold bumps (not shown) or gold balls (not shown)can be formed atop the area 920, for tape-automated (TAB) bonding orflip-chip bonding to the die.

In aggregate, the upper bond pad element 914, the lower bond pad element908, that portion of the ILD 910 between the upper and lower bond padelements, and the conductive material filling the opening 912 comprisethe "composite bond pad" 900, per se. The use of a barrier metal layer(906) underneath the bond pad (i.e., underneath the M1 layer) isoptional.

As best viewed in FIG. 9B, the bond pad 900 is generally trapezoidal, inplan view. Preferably, both the upper and lower bond pad components(elements) 914 and 908, respectively, are formed with the same geometricconfiguration, although the upper bond pad component 914 may be largerthan the lower bond pad component 908 (as shown in FIG. 9a).

Attention is directed to a peripheral region 930 (shown shaded in FIG.9b) of the lower bond pad element 908. The peripheral region 930 extendsfrom the periphery of the area of the M1 layer defined as the lower bondpad 908, to approximately less than 10% (e.g., 10 μm) towards the centerof the lower bond pad. Preferably, the peripheral region 930 is disposedentirely outside of the contact area 920. For example, if the lower bondpad element measures 100 μm across, the peripheral region may form aband only approximately 10 μm around the periphery of the lower bond padelement.

The vias 912 are illustrated in FIG. 9b as a single row ("string") offilled (916) vias extending around the periphery of the lower bond padelement, within the peripheral region 930. While shown as cylindrical(round cross-section), the vias may have any suitable cross-section,such as square, in which case they would be square columns. Thecross-sectional dimension of the filled vias 916 is preferably on theorder of 1.0-1.5 μm, and they are preferably spaced apart from oneanother by approximately 2.0-3.0 μm.

By disposing the conductive vias 912 outside of the contact area 920,bonding forces acting within the contact area are disposed substantiallyentirely over the ILD disposed between the upper and lower bond padelements, rather than over the vias (e.g., 912) between the upper andlower bond pad elements.

As best viewed in FIG. 9a, by using a plurality of small vias 912 aroundthe periphery of the bond pad, rather than the single large plug (812,FIG. 8a), the space between the upper and lower bond pad elements issubstantially entirely (i.e., 90% or more) filled with ILD oxide 910.

As in the prior art, a plurality of composite bond pads (900) aredisposed on the top surface of the die, for making a plurality ofinput/output (I/O) connections to the die.

As in the prior art, ultimately the contact area 920 is bonded to,whether with a bond wire, or by the mechanism of gold bumps/balls. Thesevarious processes typically impart mechanical and/or thermal energydirectly onto the bond pad, especially in the contact area. It has beendetermined that the "metal-ILD-metal" (i.e., 914-910-908) structure of acomposite bond pad of the present invention exhibits substantially lessbond pad lift off problems than the "metal-metal-metal" (i.e.,814-816-808) composite bond pad structure of the prior art, especiallywhen a barrier layer (806, 906) is employed. The composite bond padstructure of the present invention will thus exhibit a desirableimprovement in both assembly (packaging) yield and device reliability.

FIG. 10a shows an alternate embodiment of the invention. Two rows(strings) of filled vias are disposed all around the peripheral region1030 (analogous to 930). The inner edge of the peripheral region extendsno further inward than the contact area 1020 (analogous to 920). In theexample, the vias are shown as round in cross-section, but they could besquare or any other suitable shape. The vias in one string 1010 arepreferably offset (staggered) from the vias of the adjacent string 1012,as shown.

FIG. 10b shows yet another embodiment of the invention. A ring-like slit(through the ILD, not shown) is filled with conductive material 1016forming a continuous ring around the peripheral region 1030.

FIG. 10c shows yet another embodiment of the invention. Two elongatedslits (through the ILD, not shown) are filled with conductive material1017, 1017', on opposing sides of the peripheral region 1030.

What is claimed is:
 1. A method of laying out bond pads on asemiconductor die, each bond pad having a major axis and an orientationof its major axis, comprising:providing an array of elongated bond padshaving a tapered shape, the array of elongated bond pads along a side ofa semiconductor die; and arranging the orientation of the major axis ofeach bond pad such that the major axis aligns with an expected approachangle of a conductive line, wherein the narrower part of the taperedshape of the bond pad being toward a center area of the semiconductordie.
 2. A method according to claim 1, wherein:the side of the die is astraight edge; the orientation of the major axes of the bond pads issuch that they form a radial pattern fanning outward in a direction awayfrom the edge of the semiconductor die; and the major axes of bond padsnear a midpoint of the edge of the die have an orientation which issubstantially perpendicular to the edge.
 3. A method according to claim1, further comprising:adapting the semiconductor die to be mounted to asubstrate having conductive lines approaching a die-receiving area at arange of approach angles in a radial fan out pattern, each conductiveline corresponding to a particular bond pad on the die; and aligning themajor axis of each bond pad with the approach angle of the correspondingconductive line.
 4. A method according to claim 1, wherein:theconductive line is a bond wire.
 5. A method according to claim 1,wherein:the conductive line is a conductive trace.
 6. A method accordingto claim 1, further comprising:providing a contact footprint shape;providing an elongated tapered bond pad shape which encloses the contactfootprint shape; forming and sizing the bond pads according to theelongated tapered bond pad shape.
 7. A method according to claim 6,further comprising: providing a safety zone shape around the contactfootprint shape;wherein:the elongated bond pad shape further enclosesthe safety zone shape.